The present invention relates to cosmetic and dermatological preparations with a high UVA balance, and to the use of such preparations for increasing and/or improving the natural, endogenous UV protection system, the skin moisture and the deep moisture of the skin, the vitality and the protection of skin cells, and the use for protecting the skin against premature aging and optically perceptible changes.
The harmful effect of the ultraviolet part of solar radiation on the skin is generally known. Depending on their particular wavelength, the rays have various effects on the skin organ:
The so-called UV-C radiation with a wavelength between 100 and 280 nm is absorbed by the ozone layer in the earth's atmosphere and accordingly is not found in the solar spectrum. It is therefore of no physiological significance during sunbathing.
The so-called UV-B region is between 290 nm and 320 nm. UV-B rays are essentially responsible for the long-lasting tanning of the skin, but can at the same time cause an erythema, simple sunburn or even burns of varying severity. Chronic photodamage, photodermatoses and Herpes solaris and skin cancer can also be caused by UV-B radiation.
Since sunburn is a typical UV-B effect, many cosmetic or dermatological photoprotective products comprise UV-B filter substances as essential constituents for protecting, in particular, against sunburn. To protect against UV-B radiation, numerous compounds are known whose absorption maximum should as far as possible be around 308 nm since it is here that the erythema effectiveness of solar radiation is highest. Typical UV-B filters are, for example, derivatives of 3-benzylidenecamphor, of 4-aminobenzoic acid, of cinnamic acid, of salicylic acid, of benzophenone, and also of 2-phenylbenzimidazole.
As already explained, skin tanning is also stimulated in particular by UV-B light. Here, the melanocytes in the skin form increased melanin, which ultimately constitutes the brown coloration. This so-called delayed tanning (DT), which is generally the desired tanning, is relatively long-lasting and, moreover, also represents an endogenous UV protection.
Photoprotective products with a content of UV-B filter substances thus protect not only against sunburn, but, moreover, particularly in the case of a high sun protection factor, also slow the development of natural skin tanning.
It has for a long time been incorrectly assumed that the long-wave UV-A radiation with a wavelength between 320 nm and 400 nm has only a negligible biological effect and that, accordingly, the UV-B rays are responsible for most photodamage to the human skin. However, in the meantime, numerous studies have demonstrated that UV-A radiation is much more harmful than UV-B radiation with regard to the triggering of photodynamic, specifically phototoxic, reactions and chronic changes in the skin. The harmful effect of UV-B radiation can also be further intensified by UV-A radiation.
Moreover, much of the damage which has previously typically been attributed to UV-B light is also found following exposure to UV-A light. Thus, for example, restrictions of the cellular vitality (which can also be referred to as “cell performance” or homeostasis of the cell physiology etc.) are to be attributed to UV light generally, but particularly to UV-A light. Inter alia, in addition the subcellular organization of the cytoskeleton is also severely impaired by UV light and thus reduces the “cellular firming” of the skin. In addition, on a cellular level, the effect of UV radiation results in a large amount of damage which has to be overcome by regeneration and repair both at a protein level and also at DNA level.
In addition, sunbathing and/or exposure to sun also lead to a drying-out of the skin. This drying-out can be superficial in nature and predominantly affect the horny layer. However, it can also have a type of “deep drying-out” effect on the living cell layers of the skin. The extent of surface drying can be determined, for example, using corneometry. The extent of deep drying (the reduction in deep moisture), by contrast, can be ascertained, for example, by cell size and/or cell volume determinations of living cells in the deeper skin layers, in particular the living cells of the epidermis.
Recent findings on the effect of UV-A rays on the skin have led to increased attention now being paid to the protective measures for this ray range. Virtually no sunscreen product manages without effective UV-A filter action anymore, pure UV-B filter preparations are rare.
The UV-A content of UV light also contributes to skin tanning: immediately after exposure to UV-A light, immediate pigment darkening (IPD) arises, although this also disappears again very quickly, offers no natural UV protection and additionally represents a rather undesired grayish tan. In addition, UV-A radiation also brings about a longer-lasting tan (permanent pigment darkening, PPD) which, on account of its properties, belongs between the delayed tanning DT and the immediate tanning IPD (with significant tendencies to IPD).
A number of compounds are also known for protecting against UV-A radiation, such as, in particular, dibenzoylmethane derivatives. Further known UV-A filter substances are certain water-soluble, sulfonated UV filter substances, such as, for example phenylene-1,4-bis(2-benzimidazyl)-3,3′-5,5′-tetrasulfonic acid and its salts.
A healthy (natural) tan is viewed by the consumer as being desirable. Of importance here is not only a general “somehow darker” complexion, but rather a sporty, vital and fresh (natural) skin tanning, as is gained by gradual (gentle) sunbathing which does not lead to sunburn. The skin tanning which arises, for example, after a sunbed session is, by contrast, regarded as being unnatural or grayish. The color tone which can be achieved with self-tanning compositions as sole pigmentation carriers also barely corresponds to the color of natural healthy skin.
When applying a sunscreen composition to the skin, the ultraviolet rays can be attenuated by two effects: firstly by reflection and scattering of the rays at the surface of pulverulent solids (physical photoprotection) and secondly by absorption on chemical substances (chemical photoprotection). Depending on which wavelength range is absorbed, a distinction is made here between UV-B filters (absorption range 280 to 320 nm), UV-A filters (absorption range 320 to 400 nm) and broadband filters (absorption range 290 to about 380 nm). The group of broadband filters includes, for example, asymmetrically substituted s-triazine compounds, such as, for example, 2,4-bis{[4-(2-ethylhexyloxy)-2-hydroxylphenyl}-6-(4-methoxyphenyl)-1,3,5-triazine (INCI: Bis-Ethylhexyloxy]phenol Methoxyphenyl Triazine), certain benzophenones, such as, for example, 2-hydroxy-4-methoxybenzophenone (INCI: Benzophenone-3) or 2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol) (INCI: Methylene Bis-Benzotriazolyl Tetramethylenebutylphenol).
The use concentration of known photoprotective filter substances is currently usually determined by the composition of the cosmetic or dermatological photoprotective preparation. Accordingly, the aim of developing photoprotective products of the prior art is to achieve higher sun protection factors and/or UV-A protection performance and, in a simple and cost-effective manner, to arrive at preparations which, with the lowest possible concentrations of conventional UV filter substances, nevertheless achieve an acceptable or even high UV-A and/or UV-B protection performance. The color tone of the skin which can be achieved after use and exposure has hitherto, by contrast, played no role in developing a sunscreen product.